   #copyright

Platypus

2007 Schools Wikipedia Selection. Related subjects: Mammals

                    iPlatypus

                             Conservation status

   Least concern (LR/lc)
            Scientific classification

   Kingdom: Animalia
   Phylum:  Chordata
   Class:   Mammalia
   Order:   Monotremata
   Family:  Ornithorhynchidae
   Genus:   Ornithorhynchus
            Blumenbach, 1800
   Species: O. anatinus

                                Binomial name

   Ornithorhynchus anatinus
   ( Shaw, 1799)
   Platypus range (indicated by darker shading)
   Platypus range (indicated by darker shading)

   The platypus (Ornithorhynchus anatinus) is a semi- aquatic mammal
   endemic to eastern Australia and Tasmania. Together with the four
   species of echidna, it is one of the five species of monotremes, the
   only mammals that lay eggs instead of giving birth to live young. It is
   the sole living representative of its family ( Ornithorhynchidae) and
   genus (Ornithorhynchus), though a number of related species have been
   found in the fossil record.

   The bizarre appearance of this egg-laying, duck-billed mammal baffled
   naturalists when it was first discovered, with some considering it an
   elaborate fraud. It is one of the few venomous mammals, male platypuses
   have a spur on the hind foot which delivers a poison capable of causing
   severe pain to humans. The unique features of the platypus make it an
   important subject in the study of evolutionary biology and a
   recognizable and iconic symbol of Australia; it has appeared as a
   mascot at national events and is featured on the reverse of the
   Australian 20-cent coin.

   Until the early 20th century it was hunted for its fur, but it is now
   protected throughout its range. Although captive breeding programs have
   had only limited success and the platypus is vulnerable to the effects
   of pollution, it is not under any immediate threat.

Taxonomy and etymology

   When the platypus was first discovered by Europeans in the late 1700s,
   a pelt and sketch were sent back to the United Kingdom by Captain John
   Hunter, the second Governor of New South Wales. The British scientists
   were at first convinced that the odd collection of physical attributes
   must have been a hoax. George Shaw, who produced the first description
   of the animal in the Naturalist's Miscellany in 1799 stated that it was
   impossible not to entertain doubts as to its genuine nature, and Robert
   Knox believed it may have been produced by some Asian taxidermist. It
   was thought that somebody had sewn a duck's beak onto the body of a
   beaver-like animal. Shaw even took a pair of scissors to the dried skin
   to check for stitches.

   The common name, platypus, is Latin derived from the Greek words πλατύς
   ("platys", flat, broad) and πους ("pous", foot), meaning "flat foot".
   Shaw assigned it as a Linnaean genus name when he initially described
   it, but the term was quickly discovered to already belong to the
   wood-boring ambrosia beetle (genus Platypus). It was independently
   described as Ornithorhynchus paradoxus by Johann Blumenbach in 1800
   (from a specimen given to him by Sir Joseph Banks) and following the
   rules of priority of nomenclature it was later officially recognised as
   Ornithorhynchus anatinus. The scientific name Ornithorhynchus is
   derived from ορνιθόρυγχος ("ornithorhynkhos"), which literally means
   "bird snout" in Greek, and anatinus which means "duck-like" in Latin.

   There is no universally agreed upon plural of "platypus" in the English
   language. Scientists generally use "platypuses", "platypoda", or simply
   "platypus". Colloquially, "platypi" is also used for the plural,
   although this is pseudo-Latin. Early British settlers called it by many
   names, such as watermole, duckbill, and duckmole. The name platypus is
   often prefixed with the adjective "duck-billed" to form duck-billed
   platypus, despite there being only one species of platypus. Some of the
   names traditionally used by Australian aborigines for the platypus are
   mallangong, tambreet and boonaburra.

Description

   The body and the broad, flat tail of the platypus are covered with
   dense brown fur that traps a layer of insulating air to keep the animal
   warm. The platypus uses its tail for storage of fat reserves, an
   adaptation it shares with the Tasmanian Devil. It has webbed feet and a
   large, rubbery snout; these are features that appear closer to those of
   a duck than to those of any known mammal. The webbing is more
   significant on the front feet and is folded back when walking on land.
   Unlike a bird's beak (in which both the upper and lower parts of the
   beak separate to reveal its mouth), the snout of the platypus is a
   sensory organ with the mouth on the underside. The nostrils are located
   on the dorsal surface of the snout while the eyes and ears are located
   in a groove set just back from it; this groove is closed when swimming.
   Platypuses have been heard to emit a low growl when disturbed and a
   range of other vocalisations have been reported in captive specimens.
   A colour print of platypuses from 1863
   Enlarge
   A colour print of platypuses from 1863

   Weight varies considerably from 700 g (1.54 lb) to 2.4 kg (5.3 lb) with
   males being larger than females: males average 50 cm (20 in) total
   length while females average 43 cm (17 in). There is substantial
   variation in average size from one region to another, and this pattern
   does not seem to follow any particular climatic rule and may be due to
   other environmental factors such as predation and human encroachment.

   The platypus has an average body temperature of 31–32 °C (88–90 °F)
   rather than the 38 °C (100 °F) typical of placental mammals. Research
   suggests this has been a gradual adaptation to harsh environmental
   conditions on the part of the small number of surviving monotreme
   species rather than a historical characteristic of monotremes.

   Modern platypus young have three-cusped molars which they lose before
   or just after leaving the breeding burrow; adults have heavily
   keratinised pads in their place. The platypus jaw is constructed
   differently from that of other mammals, and the jaw opening muscle is
   different. As in all true mammals, the tiny bones that conduct sound in
   the middle ear are fully incorporated into the skull, rather than lying
   in the jaw as in cynodonts and other pre-mammalian synapsids. However,
   the external opening of the ear still lies at the base of the jaw. The
   platypus has extra bones in the shoulder girdle, including an
   interclavicle, which is not found in other mammals. It has a reptilian
   gait, with legs that are on the sides of the body, rather than
   underneath.

Venom

   The calcaneous spur found on the male's hind limb is used to deliver
   venom.
   Enlarge
   The calcaneous spur found on the male's hind limb is used to deliver
   venom.

   The male platypus has venomous ankle spurs which produce a cocktail of
   venom, composed largely of defensin-like proteins (DLPs), which is
   unique to the platypus. Although powerful enough to kill smaller
   animals, the venom is not lethal to humans, but does produce
   excruciating pain — so intense that the victim may be incapacitated.
   Oedema rapidly develops around the wound and gradually spreads
   throughout the affected limb. Information obtained from case histories
   and anecdotal evidence indicates that the pain develops into a
   long-lasting hyperalgesia that persists for days or even months. Venom
   is produced in the crural glands of the male, which are kidney-shaped
   alveolar glands connected by a thin-walled duct to a calcaneous spur on
   each hind limb. Female platypuses, in common with echidnas, have
   rudimentary spur buds which do not develop (dropping off before the end
   of their first year) and lack functional crural glands.

   The venom appears to have a different function from those produced by
   non-mammalian species: its effects are non-life threatening but
   nevertheless powerful enough to seriously impair the victim. Since only
   males produce venom and production rises during the breeding season it
   is theorized that it is used as an offensive weapon to assert dominance
   during this period.

Electrolocation

   Monotremes are the only mammals known to have a sense of
   electroreception: they locate their prey in part by detecting electric
   fields generated by muscular contractions. The platypus'
   electroreception is the most sensitive of any monotreme.

   The electroreceptors are located in rostro-caudal rows in the skin of
   the bill, while mechanoreceptors (which detect touch) are uniformly
   distributed across the bill. The electrosensory area of the cerebral
   cortex is contained within the tactile somatosensory area, and some
   cortical cells receive input from both electroreceptors and
   mechanoreceptors, suggesting a close association between the tactile
   and electric senses. The platypus can determine the direction of an
   electric source, perhaps by comparing differences in signal strength
   across the sheet of electroreceptors. This would explain the animal's
   characteristic side-to-side motion of its head while hunting. The
   cortical convergence of electrosensory and tactile inputs suggests a
   mechanism for determining the distance of prey items which, when they
   move, emit both electrical signals and mechanical pressure pulses,
   which would also allow for computation of distance from the difference
   in time of arrival of the two signals.

   The platypus feeds by digging in the bottom of streams with its bill.
   The electroreceptors could be used to distinguish animate and inanimate
   objects in this situation (in which the mechanoreceptors would be
   continuously stimulated). When disturbed, its prey would generate tiny
   electrical currents in their muscular contractions which the sensitive
   electroreceptors of the platypus could detect. Experiments have shown
   that the platypus will even react to an 'artificial shrimp' if a small
   electrical current is passed through it.

Ecology and behaviour

   The platypus is very hard to spot even on the surface of a river.
   Enlarge
   The platypus is very hard to spot even on the surface of a river.

   The platypus is semi-aquatic, inhabiting small streams and rivers over
   an extensive range from the cold highlands of Tasmania and the
   Australian Alps to the tropical rainforests of coastal Queensland as
   far north as the base of the Cape York Peninsula. Inland, its
   distribution is not well known: it is extinct in South Australia (bar
   an introduced population on Kangaroo Island) and is no longer found in
   the main part of the Murray-Darling Basin, possibly due to the
   declining water quality brought about by extensive land clearing and
   irrigation schemes. Along the coastal river systems, its distribution
   is unpredictable; it appears to be absent from some relatively healthy
   rivers, and yet maintains a presence in others that are quite degraded
   (the lower Maribyrnong, for example).

   In captivity platypuses have survived to seventeen years of age and
   wild specimens have been recaptured at eleven years old. Mortality
   rates for adults in the wild appear to be low. Natural predators
   include snakes, water rats, goannas, hawks, owls and eagles, and low
   platypus numbers in the northern Australia are possibly due to
   predation by crocodiles. The introduction of red foxes as a predator
   for rabbits may have had some impact on its numbers on the mainland.
   The platypus is generally regarded as nocturnal and crepuscular, but
   individuals are also active during the day, particularly when the sky
   is overcast. Its habitat bridges rivers and the riparian zone for both
   a food supply of prey species and banks where it can dig resting and
   nesting burrows. It may have a range of up to 7 km (4.4 mi) with male's
   home ranges overlapping with those of 3 or 4 females.

   The platypus is an excellent swimmer and spends much of its time in the
   water foraging for food. When swimming it can be distinguished from
   other Australian mammals by the absence of visible ears. Uniquely among
   mammals it propels itself when swimming by alternate rowing motion with
   the front two feet; although all four feet of the platypus are webbed,
   the hind feet (which are held against the body) do not assist in
   propulsion, but are used for steering in combination with the tail. The
   species is endothermic, maintaining its low body temperature, even
   while foraging for hours in water below 5 °C (41 °F).

   Dives normally last around 30 seconds, but can last longer although few
   exceed the estimated aerobic limit of 40 seconds. 10 to 20 seconds are
   commonly spent in recovery at the surface. The platypus is a carnivore:
   it feeds on annelid worms and insect larvae, freshwater shrimps, and
   yabbies (freshwater crayfish) that it digs out of the riverbed with its
   snout or catches while swimming. It utilizes cheek-pouches to carry
   prey to the surface where they are eaten. The platypus needs to eat
   about 20% of its own weight each day. This requires the platypus to
   spend an average of 12 hours each day looking for food. When not in the
   water, the platypus retires to a short, straight resting burrow of oval
   cross-section, nearly always in the riverbank not far above water
   level, and often hidden under a protective tangle of roots.

Reproduction

   When the platypus was first discovered scientists were divided over
   whether the female laid eggs. This was not confirmed until 1884 when
   W.H. Caldwell was sent to Australia where, after extensive searching
   assisted by a team 150 aborigines, he managed to discover a few eggs.

   The species exhibits a single breeding season, with mating occurring
   between June and October, with some local variation taking place in
   populations across the extent of its range. Historical observation,
   mark and recapture studies and preliminary investigations of population
   genetics indicate the possibility of resident and transient members of
   populations and suggest a polygynous mating system. Females are thought
   likely to become sexually mature in their second year, with breeding
   confirmed to still take place in animals over nine years old.

   Outside the mating season, the platypus lives in a simple ground burrow
   whose entrance is about 30 cm (1 ft) above the water level. After
   mating, the female constructs a deeper, more elaborate burrow up to
   20 m (66 ft) long and blocked with plugs at intervals (which may act as
   a safeguard against rising waters or predators, or as a method of
   regulating humidity and temperature). The male takes no part in caring
   for its young, and retreats to its yearlong burrow. The female softens
   the ground in the burrow with dead, folded, wet leaves and she fills
   the nest at the end of the tunnel with fallen leaves and reeds for
   bedding material. This material is dragged to the nest by tucking it
   underneath her curled tail.

   The female platypus has a pair of ovaries but only the left one is
   functional. It lays one to three (usually two) small, leathery eggs
   (similar to those of reptiles), that are about 11 mm (7/16 in) in
   diameter and slightly rounder than bird eggs. The eggs develop in utero
   for about 28 days with only about 10 days of external incubation (in
   contrast to a chicken egg which spends about 1 day in tract and 28 days
   externally). After laying her eggs, the female curls around them. The
   incubation period is separated into three parts. In the first, the
   embryo has no functional organs and relies on the yolk sac for
   sustenance. During the second, the digits develop, and in the last, the
   egg tooth appears.

   The newly hatched young are vulnerable, blind, and hairless, and are
   fed by the mother's milk. Although possessing mammary glands, the
   platypus lacks teats. Instead, milk is released through pores in the
   skin. There are grooves on her abdomen that form pools of milk,
   allowing the young to lap it up. After they hatch, the offspring are
   suckled for three to four months. During incubation and weaning, the
   mother initially only leaves the burrow for short periods to forage.
   When doing so, she creates a number of thin soil plugs along the length
   of burrow possibly to protect the young from predators; pushing past
   these on her return forces water from her fur and allows the burrow to
   remain dry. After about five weeks, the mother begins to spend more
   time away from her young and at around four months the young emerge
   from the burrow.

In mammalian evolution

   Platypus skeleton
   Enlarge
   Platypus skeleton

   The platypus and other monotremes were very poorly understood for many
   years and some of the 19th century myths that grew up around them, for
   example, that the monotremes were "inferior" or quasi-reptilian, still
   endure. It is now generally accepted that modern monotremes are the
   survivors of an early branching of the mammal tree; a later branching
   is thought to have led to the marsupial and placental groups. Although
   in 1947, William King Gregory had theorized that placental mammals and
   marsupials may have diverged earlier with a subsequent branching
   dividing the monotremes and marsupials, later research and fossil
   discoveries have suggested this is incorrect. Due to the unique
   combination of its features the platypus is also a topic in arguments
   over Darwinian evolution and intelligent design, with both sides
   claiming that its existence gives weight to their theory.

   The oldest discovered fossil of the modern platypus dates back to about
   100,000 years ago, during the Quaternary period. The extinct monotremes
   ( Teinolophos and Steropodon) were closely related to the modern
   platypus. The fossilised Steropodon was discovered in New South Wales
   and is composed of an opalised lower jawbone with three molar teeth
   (whereas the adult contemporary platypus is toothless). The molar teeth
   were initially thought to be tribosphenic which would have supported a
   variation of Gregory's theory, but later research has suggested while
   they have three cusps they evolved under a separate process. The fossil
   is thought to be about 110 million years old, which means that the
   platypus-like animal was alive during the Cretaceous period, making it
   the oldest mammal fossil found in Australia. Monotrematum
   sudamericanum, another fossil relative of the platypus has been found
   in Argentina, indicating that monotremes were present in the
   supercontinent of Gondwana when the continents of South America and
   Australia were joined via Antarctica (up to about 167 million years
   ago).

   Because of the early divergence from the therian mammals and the low
   numbers of extant monotreme species, it is a frequent subject of
   research in evolutionary biology. In 2004, researchers at the
   Australian National University discovered the platypus has ten sex
   chromosomes, compared to two (XY) found in most other mammals (for
   instance, a male platypus is always XYXYXYXYXY). Furthermore, one of
   the platypus’s Y chromosomes shares genes with the ZZ/ZW sex
   chromosomes found in birds. This news further pronounced the
   individuality of the platypus in the animal kingdom.

Conservation status

   Except for its loss from the state of South Australia, the platypus
   occupies the same general distribution as it did prior to European
   settlement of Australia. However, local changes and fragmentation of
   distribution due to human modification of its habitat are documented.
   Its current and historical abundance, however, is less well known and
   it has probably declined in numbers, although still being considered as
   common over most of its current range. The species was extensively
   hunted for its fur until the early years of the 20th century and,
   although protected throughout Australia in 1905, up until about 1950 it
   was still at risk of drowning in the nets of inland fisheries. The
   platypus does not appear to be in immediate danger of extinction thanks
   to conservation measures, but it could be impacted by habitat
   disruption caused by dams, irrigation, pollution, netting and trapping.
   The IUCN lists the platypus on its Red List as Least Concern.
   A depiction of a platypus from a book for children published in Germany
   in 1798
   Enlarge
   A depiction of a platypus from a book for children published in Germany
   in 1798

   A fungal infection poses a possible threat to platypuses in Tasmania.
   The fungus, Mucor amphiborum causes ulceration on the body that can
   lead to problems with thermoregulation and death from secondary
   infections. The same fungus so far causes no problems to the platypus
   on the Australian mainland. The Tasmania Parks and Wildlife Service and
   Biodiversity Conservation Branch Department of Primary Industries and
   Water are collaborating to monitor the effects of the infection on the
   platypus population in Tasmania. Platypuses in Tasmania tend to be
   larger than those found in the mainland of Australia, possibly because
   of the lack of introduced predators. The failure to establish the red
   fox in particular is theorized to be a contributing factor to both the
   greater average size and abundance of the platypus in the state.

   Much of the world was introduced to the platypus in 1939 when National
   Geographic magazine published an article on the platypus and the
   efforts to study and raise it in captivity. This is a difficult task,
   and only a few young have been successfully raised since — notably at
   Healesville Sanctuary in Victoria. The leading figure in these efforts
   was David Fleay who established a platypussary — a simulated stream in
   a tank — at the Healesville Sanctuary and had a successful breeding in
   1943. In 1972, he found a dead baby of about 50 days old, which had
   presumably been born in captivity, at his wildlife park at Burleigh
   Heads on the Gold Coast, Queensland. Healesville repeated its success
   in 1998 and again in 2000 with a similar stream tank. Taronga Zoo in
   Sydney bred twins in 2003, and had another birth in 2006.

In popular culture

   The platypus is sometimes jokingly referred to as proof that God has a
   sense of humor (at the beginning of the film Dogma for example). Its
   unusual appearance has led to it featuring in many media, particularly
   in its native Australia. The platypus has been used several times as a
   mascot: "Syd" the platypus was one of the three mascots chosen for the
   Sydney 2000 Olympics along with an echidna and a Kookaburra, while
   Hexley the platypus is the mascot for Apple Computer's BSD-based Darwin
   operating system, Mac OS X. A platypus named Phyl appears in several of
   the books written by Timothy Budd. Phyl is used to illustrate two
   important principles of object-oriented programming: inheritance and
   overriding. The satirist Barry Humphries exhibited the box of a mock
   pesticide product called "Platytox" during his early surrealist period.
   Experimental rock band Mr. Bungle has a track named after the creature
   on their second major album, Disco Volante.

   Platypuses are frequently seen in children's cartoons: a platypus named
   Ovide was the star of the cartoon Ovide and the Gang; two platypuses
   appear in the cartoon Taz-Mania; a young platypus named Flap is a
   regular character in each of the Blinky Bill cartoon series; and in the
   animated show Camp Lazlo, the character of Edward is a platypus. In
   1995, United Paramount Network broadcast a short-lived television
   series entitled Platypus Man, starring comedian Richard Jeni. The title
   came from a joke, repeated at the beginning of each episode, comparing
   the platypus' solitary behaviour with the lead character's personal
   life.

   Retrieved from " http://en.wikipedia.org/wiki/Platypus"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
